Mineral fibres made by melting and centrifuging of mineral raw materials, such as stone, slag, glass, ceramics or the like, are extensively used for the manufacture of mineral fibre mats and blankets, primarily for heat and sound insulation purposes, especially within the construction industry. Such mineral fibre products conventionally contain a binder, of which a number of different types are known.
Thus for example, phenol cured insulating products are known. Phenol is a fairly inexpensive and also a rapidly curing binder. A phenol cured product resists temperatures up to 250° C., but the bonds are destroyed if the temperature is maintained above 250° C. for an extended period of time. At higher temperatures, at 400° C. and more, the binder loses its strength, the temperature increases rapidly and the product collapses. In addition, a phenol cured insulating product emits poisonous gases during burning. An additional and also major disadvantage is that the presence of phenol in the product will cause an undesired load on the environment when the binder-containing mineral wool product is to be disposed of after use.
Also water glass has been widely used as a binder. Water glass is traditionally made by melting silica sand with sodium or potassium carbonate at a very high temperature and then dissolving the finely divided solidified product in water. Thus water glass can be considered an ecologically acceptable substance to include as a binder in mineral wool products. A disadvantage is, however, that the manufacture thereof uses pure raw materials and is energy consuming.
It is also known to use a mixture of water glass and clay as a binder for mineral wool products, see e.g. SE 420 488. Such a product, although providing good water and heat resistance, has poor compression resistance, is brittle and causes dusting. The EP B 466 754 on the other hand describes the use of a binder made from slag and water glass for making a temperature and moisture resistant mineral wool product which is also capable of withstanding high temporary loads.
The international application WO 01/00916 discloses a binder for mineral wool products, which is made by dissolving a particulate glassy mineral material in an aqueous solution, nucleating and stabilizing the so obtained solution to form a binder solution in the form of a sol, and applying the so obtained binder to mineral fibres in order to bind the same. The aqueous solution can be an alkaline or an acidic solution. The sol so obtained can be made to gel, either before application, for example by changing pH or adjusting the electrostatic repulsion between the particles in the solution, or gel formation of the sol is brought about after having been applied to the mineral fibres.
The object of the present invention is to provide an easy and economically feasible method for binding mineral wool products, which binder has excellent binding and fire resistant properties and is acceptable from a use or occupational health point of view. An important advantage is that the binder used according to the invention presents no ecological load on the environment, but contains only such components that are already inherently present in the mineral wool product.